Ultrafast calculation of diffuse scattering from atomistic models

Paddison, Joseph A. M.

doi:10.1107/s2053273318015632

Cited by 34 publications

(34 citation statements)

References 53 publications

(100 reference statements)

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“…See the Supporting information for simulations with other values of J 2 /J 1 . The scattering patterns of the configurations were calculated using the software Scatty (Paddison, 2019) with Nb on the positions of the occupied X sites. X-ray scattering factors were used.…”

Section: Methodsmentioning

confidence: 99%

A simple model for vacancy order and disorder in defective half-Heusler systems

Roth

Zhu

Iversen

2020

IUCrJ

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Defective half-Heusler systems X 1−x YZ with large amounts of intrinsic vacancies, such as Nb1−x CoSb, Ti1−x NiSb and V1−x CoSb, are a group of promising thermoelectric materials. Even with high vacancy concentrations they maintain the average half-Heusler crystal structure. These systems show high electrical conductivity but low thermal conductivity arising from an ordered YZ substructure, which conducts electrons, while the large amounts of vacancies in the X substructure effectively scatters phonons. Using electron scattering, it was recently observed that, in addition to Bragg diffraction from the average cubic half-Heusler structure, some of these samples show broad diffuse scattering indicating short-range vacancy order, while other samples show sharp additional peaks indicating long-range vacancy ordering. Here it is shown that both the short- and long-range ordering can be explained using the same simple model, which assumes that vacancies in the X substructure avoid each other. The samples showing long-range vacancy order are in agreement with the predicted ground state of the model, while short-range order samples are quenched high-temperature states of the system. A previous study showed that changes in sample stoichiometry affect whether the short- or long-range vacancy structure is obtained, but the present model suggests that thermal treatment of samples should allow controlling the degree of vacancy order, and thereby the thermal conductivity, without changes in composition. This is important as the composition also dictates the amount of electrical carriers. Independent control of electrical carrier concentration and degree of vacancy order should allow further improvements in the thermoelectric properties of these systems.

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Section: Methodsmentioning

confidence: 99%

A simple model for vacancy order and disorder in defective half-Heusler systems

Roth

Zhu

Iversen

2020

IUCrJ

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“…Monte-Carlo simulations of the structure were performed using the Metropolis algorithm (Metropolis et al, 1953) using a custom python script. The model scattering was calculated using the Scatty software (Paddison, 2019) and the model 3D-ÁPDF was obtained by Fourier transforming the model scattering using a custom python script.…”

Section: Simulated Datamentioning

confidence: 99%

Tuneable local order in thermoelectric crystals

Roth

Beyer

Fischer

et al. 2021

IUCrJ

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Although crystalline solids are characterized by their periodic structures, some are only periodic on average and deviate on a local scale. Such disordered crystals with distinct local structures have unique properties arising from both collective and localized behaviour. Different local orderings can exist with identical average structures, making their differences hidden to Bragg diffraction methods. Using high-quality single-crystal X-ray diffuse scattering the local order in thermoelectric half-Heusler Nb1−x CoSb is investigated, for which different local orderings are observed. It is shown that the vacancy distribution follows a vacancy repulsion model and the crystal composition is found always to be close to x = 1/6 irrespective of nominal sample composition. However, the specific synthesis method controls the local order and thereby the thermoelectric properties thus providing a new frontier for tuning material properties.

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“…Two regions near Q ≈ 1.2 and 1.5 Å −1 have been excluded from the final refinements: the first is related with the magnetic peak from possible MnO impurity, which is present in the data up to 70 K; and the second due to the up-down features in the area of the intense nuclear reflection. The resulting spin configurations were used to reproduce the reciprocal space maps using the SCATTY program [29]. The (hk0.5), (h0.5l ), and (0.5kl ) scattering planes are shown in Figs.…”

Section: Diffuse Scattering and Short-range Magnetic Orderingmentioning

confidence: 99%

Long-range magnetic ordering in Li2MnGeO4 and precursor short-range spin correlations

et al. 2020

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Long-range magnetic ordering and short-range spin correlations in layered noncentrosymmetric orthogermanate Li 2 MnGeO 4 were studied by means of polarized and unpolarized neutron scattering. The combined Rietveld refinement of synchrotron and neutron powder diffraction data at room temperature within the Pmn2 1 space group allowed us to specify the details of the crystal structure. According to the additional Bragg peaks in low-temperature neutron diffraction patterns a long-range antiferromagnetic ordering with the propagation vector k = (1/2 1/2 1/2) has been found below T N ≈ 8 K. Symmetry analysis revealed the model of the ground state spin structure within the C a c (no. 9.41) magnetic space group. It is represented by the noncollinear ordering of manganese atoms with a refined magnetic moment of 4.9 μ B /Mn 2+ at 1.7 K, which corresponds to the saturated value for the high-spin configuration S = 5/2. Diffuse magnetic scattering was detected on the neutron diffraction patterns at temperatures just above T N . Its temperature evolution was investigated in detail by polarized neutron scattering with the following XYZ-polarization analysis. Reverse Monte Carlo simulation of diffuse scattering data showed the development of short-range ordering in Li 2 MnGeO 4 , which is symmetry consistent on a small scale with the long-range magnetic state below T N . The reconstructed radial spin-pair correlation function S(0) S(r) displayed the predominant role of antiferromagnetic correlations. It was found that spin correlations are significant only for the nearest magnetic neighbors and almost disappear at r ≈ 12 Å at 10 K. Temperature dependence of the diffuse scattering implies short-range ordering long before the magnetic phase transition. Besides, the spin arrangement was found to be similar in both cases above and below T N . As a result, an exhaustive picture of the gradual formation of magnetic ordering in Li 2 MnGeO 4 is presented.

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Ultrafast calculation of diffuse scattering from atomistic models

Cited by 34 publications

References 53 publications

A simple model for vacancy order and disorder in defective half-Heusler systems

A simple model for vacancy order and disorder in defective half-Heusler systems

Tuneable local order in thermoelectric crystals

Long-range magnetic ordering in Li2MnGeO4 and precursor short-range spin correlations

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